Dibenzoylmethane derivatives such as 4-tert-butyl-4'-methoxy-dibenzoylmethane (PARSOL 1789) absorb UV-A radiation quite significantly and effectively up to 380 nm. However, no UV-A blocking sunscreen can be used alone if absorbtion in a wide band of UV-radiation is required. Thus, UV-A filters usually must be combined with an UV-B absorbing agent. Most popular is the combination of 4-tert-butyl-4'-methoxy-dibenzoylmethane with 2-ethylhexyl-p-methoxycinnamate (PARSOL MCX). Such a combination is described in U.S. Pat. No. 4,387,089. Many customary preparations contain a combination of PARSOL 1789 and PARSOL MCX.
As dibenzoylmethane derivatives are photolabile it is necessary to photostabilise these UV-A filters.
Cosmetic light-screening compositions based on dibenzoylmethane derivatives as UV-A filter and photostabilised with 3,3-diphenylacrylate derivatives are described in the European patent publication EP-0 514 491 B1. Said known compositions comprise at least one fatty phase, 1-5 wt % of a dibenzoylmethane derivative and at least 1 wt % of a 3,3-diphenylacrylate derivative. The mole ratio of the 3,3-diphenylacrylate derivative to the dibenzoylmethane derivative is not less than 0.8 and not more than 8. Said light-screening compositions may contain, in addition, water soluble LV-B screening agents like 2-phenyl-benzimidazole-5-sulfonic acid (PARSOL HS), terephthalydene-3-3'-dicamphor-10,10'-disulfonic acid (MEXORYL SX) and water-soluble UV-A screening agents like 2-hydroxy-4-methoxy-benzophenone-5-sulfonic acid, (UNIVUL MS-40). However, cinnamic acid derivatives are not mentioned.
The European patent publication EP 0 780 119 A1 describes a photostable, cosmetic light-screening composition comprising at least one fatty phase, 0.1-5 wt % of a dibenzoylmethane derivative and 0.5-4.5 wt % of a 3,3-diphenylacrylate derivative as stabilizer. The mole ratio of the 3,3-diphenylacrylate derivative to the dibenzoylmethane derivative is less than 0.8. Said light-screening compositions may contain, in addition, polysiloxane derivatives, polyacrylate derivatives or microfine metal oxides as UV-B filters. However, cinnamic acid derivatives are not mentioned.
Cosmetic light-screening compositions based on dibenzoylmethane derivatives as UV-A filter and photostabilised with benzylidene camphor derivatives are described in U.S. Pat. No. 5,605,680. Said known compositions comprise at least one fatty phase, 1-3 wt % of 4-tert-butyl-4'-methoxy-dibenzoylmethane and at least 4.5 wt % of p-methylbenzylidene camphor. The weight ratio of the p-methylbenzylidene camphor to the 4-tert-butyl-4'-methoxy-dibenzoylmethane is greater or equal to 3. Additional UV-A or UV-B filters are not mentioned in this patent publication.
A large number of popular broadband light screening compositions are based on PARSOL MCX and PARSOL 1789 as essential UV-B and respectively, UV-A filters. Additional UV filters are optional. In many such cases, the stabilisation of PARSOL 1789 by octocrylene as suggested in the above mentioned European patent publications EP-0 514 491B1 and EP-0 780 119 A1 is not sufficient. The stabilisation of PARSOL 1789 by p-methyl-benzylidene camphor as suggested in the above mentioned U.S. Pat. No. 5,605,680 is also not sufficient.
It has now been found that a light screening composition comprising a dibenzoylmethane derivative as UV-A filter, a water-soluble p-methoxy-cinnamate derivative as UV-B filter and a 3,3-diphenylacrylate derivative or a benzylidene camphor derivative as stabilizer shows a surprisingly higher photostability compared to a corresponding light screening composition containing the commonly used PARSOL MCX as UV-B filter.